Electrophotographic or laser printers have been commercially available for several years and are known to provide some of the highest forms of print quality on the printed media in all of the fields of both impact and non-impact printing. An example of these laser printers is the Hewlett-Packard LaserJet Series II printers which are described in the LaserJet Series II User's Manual, part number 33440-90901 available from the Hewlett-Packard Company (HP) of Palo Alto, Calif. These Hewlett-Packard LaserJet Series II printers include, among other things, means for receiving user input printer language commands via a computer interface cable, means for interpreting these user input printer language commands such as the Hewlett-Packard Printer Command Language (PCL), and means connected to these interpreting means for accessing the appropriate digital data from printer memory. This digital data is accessed and processed in order to obtain corresponding printable character data representative of a particular size, treatment (e.g., style and stroke weight), and print orientation. This type of character data is also known in the art as bitmap data. This character data is in turn used for controlling a laser beam of the laser printer, and the laser beam in turn is operative to write a printed image on a photoconductive drum of the laser printer. The printed image is then transferred from the photoconductive drum to an adjacent print media as is well known in this art.
As used herein and as is generally understood in this art, the term "typeface" is defined as a group of characters that have similar design features. Often a typeface will be available in several treatments, e.g., bold, italic, etcetera. Within the HP LaserJet Series II and all other HP PCL printers, characters within a typeface are accessed by a user through character sets. The term "character set" as used herein and as is generally understood by those skilled in the art is defined as a grouping of characters, generally containing many less characters than all characters designed for typeface, and arranged with a specific printer application in mind. For example, the legal and math character sets are generally designed to support legal and scientific applications, and they contain only those characters used in the particular application (e.g., there is no square root character in the legal character set).
Whereas these HP LaserJet Series II printers have been highly regarded and widely accepted by consumers throughout the world as the latest in state-of-the-art laser printing technology, these laser printers nonetheless have an upper limit on the number of characters in unique character sets and typeface treatments which are available from a given amount of memory storage capacity of the printer. This memory for the HP LaserJet Series II printer is read-only-memory (ROM).
One reason for this upper limit on the memory for character storage capability of the HP LaserJet Series II printer is that this printer was designed so that each character of each typeface in each treatment and for each size was stored separately in memory and represented with unique digital data (i.e., bitmap data) therein. This was true even though certain characters are common across multiple typefaces and typeface treatments. This latter design characteristic of the HP LaserJet Series II printer obviously required a significant duplication of memory storage for identical characters in the different available typeface treatments.
The above duplication of ROM memory storage is undesirable for a number of reasons. Firstly, the requirement for additional ROM to add character storage capability to a laser printer can mean an additional ROM cost of between $9.00 and $12.00 per ROM semiconductor chip. When this additional cost is multiplied by a standard manufacturing cost multiplier of typically between 3 and 4, this can mean adding as much as $50.00 to the consumer cost in an extremely competitive marketplace.
Secondly, the requirement for adding more ROM memory capability to a laser printer means the addition of more pins on the printed circuit board which supports the ROMs, and this in turn means lowering printer reliability. Thus, the high desirability of minimizing memory storage (ROM) requirements in laser printers while simultaneously maximizing the character storage capability of the printer is manifest.